Process for recovering 4-nitro-2-amino-toluene from its nitration mixture



Patented Apr. 23, 1935 PROCESS FOR RECOVERI NG 4 -Nrrao-2- AMINO-TOLUENE FROM ITS NITRATION MIXTURE I John M. Tinker, South Milwaukee, Wis., and Willate! 0. Stewart, Preston, Iowa, assignorsto E.

- I. du Pont de Nemours & Company, Wilmington, Del.,.a corporation of Delaware No Drawing, Application February 5, 1932;

' Serial No. 591,240

, Claims. (erase-130.5)

This invention relates to a process for purifyof the nitration mass by conversion into a salt of log. p nitro-o-toluidine (CH3INH 2ZNO2=1:2:4)'. an aryl sulfonic acid. It appears that aryl sul- It is an object of thisinvention to provide an ecofonates of l-nitro-2-toluidine are considerably nomical. and eflicient process for separating pless soluble' than the corresponding sulfonates of nitro-o-toluidine from isomers or other nitro the other isomers, and also less soluble than the i bodies formed therewith in the nitration of o sulfate of 4-nitro-2-to1uidine. As a result, both toluidine by reacting upon the same with nitric the precipitation of l-nitro-Z-toluidine from the acid in a medium of sulfuric acid. nitration mass is more complete than, and its sep- Other and further important objects of this aration from the other isomers is at least as good I w invention will appearas the description proceeds. as in the case'of precipitation by the shulfate 1o By p-rlitro-o-toluidine We are referring her'emethod.

in to the following compound: Many and various aryl sulfonic acids may be CH3 7 used for our purpose, including those of the ben e I zene, naphthalene and anthraquinone series. For 15v practical purposes,however, the sulfonic acids of 15 i c I naphthalene are most advantageous, since-these 5 1 g V a can be obtained readily and more economically 4 I than the others It is not necessary for our pur- NO2 I pose to use chemically isolated sulfonic acids of This compound, which may also be designated naphthalene since" either or flilaphthalene 20 t 2 n or d d sulfonic acid or various disulfonic acids of naphis a valuable intermediate for dyestuffs. It is thaleneere effective our perposei it m genemny prepared in theartby reacting i econom cal to use the sulfonatlon mass directly nitric-sulfuric-acid mixture upon o-toluidine in as Obtained in sulfonaimg naphthalene 7 2 5 a medium of concentrated sulfuric acid (Beils'tein, The above results e notto'loe e n $111.08 4th Ed., XII, 844) This process leads to a prodthere appears to be 110 e, y which to Pr the uct consisting mainly of -nitl'o-Z-toluidine, but fiolubilities of alyl-sulfonate of various containing. also some quantities of m aromatic amines. Nor was it tobe foreseen that toluidine and small amounts of the 5-nitro-isothe Various naphthalene SHIfOHatQSOf4-mtYO-Z- 3 mer. -The method used in the art for separating tow-mine and 5'nitro'z-teluidine w i e e these was based on the diffe ent solubiliti'es'of respects their solubilities along the same line as 7 their sulfates. The sulfate of the l-isomer is any Particular naphthalene sulfenete of h e considerably less soluble in cold dilute sulfuric aminesrwith the resultant advantage theta acid. than that of. the fi-isomelx. Separation was ture o naphthalene Sulfonates y be used to 5 therefore effected by fractional precipitation of efieet Separation instead of Pertleular Single the sulfates from the cooled and diluted sulfuric sulfonatei s c a acid solution in whichthey are formed, and fur,- It has been knowninrthe art to m y a ther recrystallization from alcohol (ibid). Salts of various naphthalene-sulfonic' acids to This methoihowever, has the disadvantage effect separation of e latter f a other 40 that large quantities of the ii-isomer r l t d (Jour. Soc. Chem. Ind, Vol. 43, pages 299-303T). 40

to its residual solubility in the mother'liguors. In This p e that the Salts, of given a y ne other Words, whatever amounts of. 4-nit'ro-2- and two different naphthalene sulfonic acids diftoluidine sulfate are precipitated are substanfe 'ed in thc fi sufficiently o'e 's patially free of isomers, but not all the I-nitro-Z- ration of the two. Thereverse, however, was not toluidine in the original solution is so precipitatto be foreseen. Namely, it ,Was not to be fore 45 ed. The process is, therefore,' astefui of the deseen that the salts formedby a given naphthalene v sired main product. T I sulfonic acid and two isomeric arylamines, more We have now found that the l-nitro isomer particularly, the ,4? and d-nitro-Z-toluidines, formed. in the above process of nitration can be would differ sufficiently in their solubilitie's to very efiectively and economically precipitated out enable separation. I I V 50.

The reaction between the mixture of nitrotoluidines and the naphthalene sulfonic acids may be effected in any convenient manner, for instance by diluting the respective reaction masses, that is, the nitration mass of toluidine and the sulfonation mass of naphthalene, without troubling to isolate the solid products.

If desired, a water soluble salt of the aryl-sulfonic acid may be used in lieu of the free acid; again, a mixture of the two may be employed.

After the precipitated aryl-sulfonate of p-nitroo-toluidine has been isolated, it may be neutralized with alkali (suchas caustic alkali, sodium carbonate, or ammonia) to give the free base of p-nitro-o-toluidine and the corresponding salt of the aryl-sulfonic acid. The former is insoluble in the neutralized mass and may be recovered by filtration, while the mother liquors may be reused for precipitating p-nitro-o-toluidine from a subsequent nitration batch.

Without limiting our invention to any particular procedure, the following example is given to illustrate our preferred mode of operation. Parts given are parts by weight.

Example A finished nitration mass as obtained from 214 parts of o-toluidine, and containing about 1000 parts of concentrated sulfuric acid is poured into 4000 parts of cold water. The temperature may be allowed to rise to -50 C. A solution of naphthalene 1,5- and 1,6-disulfonicacid as obtained by sulfonating 140 parts of naphthalene with 25% oleum at 20-40" C. and diluting the finished sulfonation with water, is now added. The entire mass is diluted with water to a total of about 10,000 parts. It is then stirred for 12-15 hours at room temperature and filtered. The filter cake is washed well with 7500 parts of cold water.

The washed salt is stirred with a hot solution of 130 parts of soda ash in 5000 parts of water at about 45-50 C. It is then cooled to room temperature, filtered and washed. The filter cake is dried at 75-80" C., and yields 234 parts of 4- nitro-Z-amino-toluene in the form of a light ye1- low powder, melting at 106.6-107.0 C. The recovery thus amounts to substantially 9095% of all the p-isomer formed in this nitration process.

The recovered mother liquor contains the sodium salt of naphthalene-disulfonic acid and may be used instead of the free acid for precipitation of 4-nitro-2-toluidine in the next nitration batch.

For best results, it is preferably fortified with a quantity of fresh naphthalene-disulfonic acid, or a water-soluble salt thereof, corresponding to 43 parts of naphthalene. V 5

If desired, naphthalene-monosulfonic acid (0:, B, or a mixture of the two) may be used for precipitation instead of the disulfonic acid. In this case a quantity of monosulfonic acid (or a salt thereof) corresponding to 198 parts of naphthalene' are needed for the first batch, and a quantity corresponding to 47 parts of naphthalene should preferably be used in addition to'the basic mother liquor from the previous hydrolysis step, in each subsequent batch.

In general, the quantity of aryl-sulfonic acid body to be added can be determined stoichiometrically from an analyzed sample of the nitration mass. A simpler method, however, is to add aryl sulfonate to the nitration mass until a small sample thereof, filtered at room temperature, gives no further precipitate with additional arylsulfonic acid. Excessive quantities of aryl-$11.1

fonic acid have no harmful effects on the process except that they constitute waste.

The temperature of the mass during the first filtration step should preferably be about room temperature or lower, to prevent solution of undue amounts of the 4-nitro-2toluidine-aryl-sulfonate in the mother liquor. However, considerable variation is permissible either way, as long as a test does not show the mother liquors to contain more than about 18 to 20% of the total quantity of nitro-toluidines formed. Similarly, excessive washing of the filter cake may carry 01f some of the desired product. The washing should therefore not be carried beyond the point at which a sample of the filter cake, when based, refiltered and dried, has a melting point of 106.6 107.0 C.

Many variations and modifications are possible in our preferred mode of procedure without departing from the spirit of this invention.

In the claims below it should be understood that by the term sulfonic acid body we intend to cover the isolated sulfonic acid, salts thereof, and the crude sulfonation mass in which these may be produced.

. We claim:

1. In the process of preparing 4-nitro-2-amino-.

toluene by nitrating o-toluidine in concentrated sulfuric acid, the step which comprises reacting the diluted nitration mass with an aryl-sulfonic acid body. v

2. In the process of preparing -nitro-Z-aminotoluene by nitrating o-toluidine in concentrated sulfuric acid, the step which comprises reacting the diluted nitration mass with a water soluble aryl-sulfonic acid body, and recovering the precipitated mass.

3. A process as in claim2, in which the arylsulfonic acid body is a mixture of naphthalene sulfonic acids and their'water-soluble salts.

4. A process as in claim 2, in which the arylsulfonic acid body is a mixture of naphthalene sulfonic acids. ,7

5. In the process of preparing 4-nitro-2-aminotoluene by nitrating o-toluidine in concentrated sulfuric acid, the steps which comprise reactin the diluted nitration mass with an water soluble aryl-sulfonic acid body, filtering off the precipitated aryl-sulfonate of 4-nitro-2-amino-toluene and hydrolyzing the same in alkaline solution to recover 4-nitro-2-amino-toluene. r

6.. A process for preparing 4-nitro-2-amino toluene in a form substantially free of isomers, which comprises mono-nitrating o-toluidine in concentrated sulfuric acid, diluting the reaction mass with water, adding an aqueous solution of aryl sulfonic acid compounds, filtering, reacting upon the filter cake with hot aqueous alkali, cooling and recovering the precipitated 4-nitro-2- amino-toluene.

7. A process for preparing 4-nitro-2-aminotoluene in a form substantially free of isomers, which comprises mono-nitrating o-toluidine in concentrated sulfuric acid, diluting the reaction mass, with water, adding an aqueous solution of naphthalene sulfonic acid compounds, filtering, reacting upon the filter cake with hot aqueous alkali, cooling and recovering the precipitated 4-nitro-2-amino-toluene.

8. In the process of preparing 4-nitro-2-aminotoluene by nitrating o-toluidine in concentrated sulfuric acid, the steps which comprise reacting the diluted nitration mass with a water-soluble aryl-sulfonic acid body, filtering off the precipitated aryl-sulfonate of 4 nitro-2-amino-toluene cover4-nitro-2-amino-toluene.

9. In the process of preparing 4-nitro-2-aminotoluene by nitrating o-toluidine in concentrated sulfuric acid, the step which comprises reacting the diluted nitration mass with a water soluble aryl-sulfonic acid body.

10. In the process of preparing 4-nitro-2- amino-toluene by nitrating o-toluidine in con-- centrated sulfuric acid, the step which comprises reacting the diluted nitration mass with a water soluble aryl-sulfonic acid body selected from the benzene, naphthalene and anthraquinone series.

JOHN M. TINKE f WILLARD c. STEWART. 

